Plasminogen Activator Inhibitor 2: Expression and Role in Differentiation of Epidermal Keratinocyte*1

Plasminogen activator inhibitor 2 (PAI-2) is an enzyme inhibitor which is involved in cell differentiation, tissue growth and regeneration. In this study, immunocytochemistry, in situ hybridization and confocal laser scanning microscopy were used to investigate the expression and role of PAI-2 in differentiation of keratinocytes in vitro. The result showed that in the mono-layer differentiated keratinocytes induced by high calcium concentration, the expression of PAI-2 and its mRNA increased significantly, accompanied by expression increase of the differentiation marker keratin 10; and in the multi-layer differentiated keratinocytes induced by high calcium, PAI-2 expressed strongly mainly in the keratinocytes of middle as well as upper stratified layers, while K10 expressed in the keratinocytes of all stratified layers. Furthermore, the changes of the parameters related to keratinocyte differentiation were detected after inhibition of PAI-2 functions by its antibody, and the data showed that when treated by PAI-2 antibody, involucrin in the keratinocytes envelope expressed increasingly with an altering distribution from part to the whole envelope area. Our results indicate that during differentiation of epidermal keratinocyte, PAI-2 expresses mainly in the more differentiated keratinocytes and may protect the terminal differentiated keratinocytes from prematuration through inhibiting involucrin expression in cornified envelope.